1. Field of the Invention
The present invention relates to a facsimile apparatus, and more specifically to a transmission mode of a modem provided therein.
2. Description of the Prior Art
Recommendation V.34 of ITU-T (International Telecommunications Union-Telecommunications Standardization Sector), which was made in 1994, recommends a transmission procedure of a modem for use in a facsimile apparatus. Hereinafter, Recommendation V. 34 of ITU-T is referred to as V. 34. V. 34 is formally referred to as “The operation of modems at the data rate up to 28,800 bit/s for use in a telephone network or a 1—1 dedicated line in 2 line system.” According to V. 34, the transmission at the rate up to 28,800 bps is advised to be achieved by measuring a line condition used therefor and adjusting parameters therefor based the line condition. The facsimile apparatus pursuant to V. 34 has a transmission control procedure according to the binary control procedure of Recommendation T. 30 “The procedure of facsimile transmission in a general telephone exchange network.” To mutually confirm an operating procedure between an origination facsimile apparatus and a destination facsimile apparatus, the binary control procedure employs a frame structure of the High Level Data Link Control (HDLC) designed for data transmission.
The above facsimiles are provided with functions satisfying ITU-T Recommendation V. 8. Hereinafter, ITU-T Recommendation V. 8 is referred to as V. 8. V. 8 proposes a connection sequence of modems. According to V. 8, modems select from among several modes one that they utilize for transmission. Since the selection pursuant to V. 8 is essential for the procedure of V. 34, modems pursuant to V. 34 must be provided with functions of V. 8.
The facsimile having a modem with functions of V. 8 and V. 34 will be described below. In the event of transmission of information from an origination facsimile apparatus to a destination facsimile apparatus, prior to the Fax Handshaking procedure recommended by Recommendation T. 30 of ITU-T after establishment of a line therebetween, the modems in the facsimile apparatuses have a given sequence of implementing a negotiation, or an exchange of information to determine a transmission mode by themselves and thus, independent of a CPU (Central Processing Unit). This sequence of the negotiation corresponds to Phase 2 in V. 34 discussed below.
The modems having functions of V. 8 and V. 34 perform the following four phases: Phase 1 in V. 8, and Phases 2–4 in V. 34. During the phases, the modems remeasure the line condition and decide the parameters on modulation.
Next, Phase 2 in V. 34 will be described. According to Phase 2 in V. 34, fundamental items therein are set through probing the line and exchanging the parameters for modulation. First, in Phase 1 in V. 34, the connection between the origination modem and the destination modem starts. Thereafter, in Phase 2 of V. 34, after selecting a communication to mode according to V. 8, an exchange of the parameters on modulation is carried out between the origination modem and the destination modem. Subsequently, the origination modem sends a line probe signal for measurement of the line condition, which allows information to be exchanged on a symbol rate, a pre-emphasis, an available data rate, a carrier frequency, and a transmission level to be exchanged based upon the line condition and the INFO data. Thus, Phase 2 in V. 34 is completed, which commences Phase 3 in V. 34. Phase 2 in V. 34 will be discussed more specifically below. As explained above, it is the modems that execute the negotiation. Upon a failure to accomplish the negotiation, the modems spontaneously carry out a retrain, that is, a trial of another negotiation. However, if the line condition is bad due to a poor line or noise, for example, the modems cannot accomplish the negotiation. As long as the line condition is unchanged, the modems try retraining repeatedly.
Since the negotiation is independent of the CPU, the CPU does not assist the modems in performing the negotiation. To avoid repetition of retraining with the line connected, a timer monitors the period of Phase 2 of V. 34. If Phase 2 of V. 34 fails to be completed within a given period of time, the CPU disconnects the line as a communication error.
The facsimile apparatuses with such a timer can avoid the repetition of retraining over the connected line. However, every negotiation of the facsimile apparatuses through redialing after disconnection of the line fails while the line condition remains unchanged, which poses a problem that the facsimile apparatuses cannot complete Phase 2 of V. 34.